A process for forming an improved durability thick ceramic coating on a substrate, such as a turbine engine component, is described.
Thick ceramic abradable seal coatings for high turbine applications have shown deterioration and spallation in applications that run hotter than earlier engine generations. Cracking in thick ceramic coatings is initiated at the hot surface of the coating where sintering begins. Sintering shrinkage causes planar tensile stresses which cause the cracking. Sometimes, the cracking takes the form of mudflat cracks. This type of cracking propagates perpendicular to the stress until a change in anisotropic coating properties and stresses causes crack deflection. Sintering shrinkage as a function of time shows rapid initial densification that is associated with the elimination of the smallest porosity and microstructural defects, i.e. splat boundaries, micro-cracks, and fine porosity.